This application claims the priority of German application 199 16 478.9, filed in Germany on Apr. 13, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process and system for evacuating a reactor, in which process at least one object is sterilized by means of low pressure plasma, from atmospheric pressure to plasma discharge pressure.
Reactors of this type are prior art in, for example, U.S. Pat. No. 3,701,628. Here it can be necessary to evacuate the reactor to pressures which lie in the range of fractions of a millibar.
The sterilizing effect of a plasma is based on its mechanical destruction of the bacteria by means of ion bombardment as well as on the chemical destruction by means of the occcurring radicals. Using only low energy requirements, the plasma can penetrate into the smallest surface cracks and holes, whereby with increasing vacuum the temperature can be reduced to such a low point that even heat sensitive objects, for example bottles made of plastic, can be processed.
In the case of sterilizing for example the inner surface of containers, the container inner pressure must, before the plasma phase begins, be reduced from atmospheric pressure (1000 mb) to plasma discharge pressure (for example 0.2 mb) If in the case of an industrial installation, a plurality of containers, and thus reactors, are to be evacuated within the shortest possible time, then volumes of gas, which can easily reach thousands of liters per second at the level of the plasma discharge pressure, must be pumped out. This leads to huge practical problems.
It is an object of the present invention to pump out, even at the lowest plasma discharge pressures, large amounts of gas in evacuable reactors cost-effectively and easily.
This object has been achieved in accordance with the present invention in that two successive but separate evacuating stages are provided, whereby the reactor is evacuated in the first evacuation stage to an intermediary pressure and at least to the plasma discharge pressure in the last evacuation stage.
Thus, instead of a one-stage evacuation, a so-called differential evacuation takes place. Vacuum pumps can be applied for each evacuation stage, said pumps being particularly efficient for the relevant pressure range. The individual pumps are activated parallel to one another, so that they deliver different mass flow. By means thereof, most of the gas volume to be pumped, for example 97%, is pumped out during the first evacuation stage, so that this amount is guided past at the second and at a possible third evacuation stage, which then function at a low pressure level. This saves the latter mentioned pumpsxe2x80x94from the viewpoint of its pressure levelxe2x80x94from having to handle huge volumes of gas. It should be mentioned here, that in the case of a gas expanding to an increasingly smaller pressure, the volume of the gas increases by the relevant factor.
A separate vacuum chamber is advantageously provided for every evacuation stage, to which the reactor is respectively connected. For example, three vacuum chambers can be provided which work at different pressure levels.
The following is an example:
In a first evacuation stage, the respective reactor can be pumped from atmospheric pressure to an intermediary pressure of 30 mb. In a further evacuation stage, the pressure level is brought down to 1.3 mb. In the subsequent third and last evacuation stage, the plasma discharge pressure of, for example, 0.2 mb is reached. By means of this differential evacuation, only a few hundred liters of gas volume per second is pumped off per evacuation stage. Without this differential pumping, the pump would have to transport several thousand liters of gas per second.
This pressure level reached in the last evacuation stage is maintained until the end of the serialization process, that is, during the entire plasma phase.
In the case of an arrangement for carrying out the process, a plurality of reactors can be provided, which are each provided with devices for taking up at least one container to be sterilized and to which at least two vacuum chambers of differing pressure levels are arranged, to which the reactors can be connected successively by means of valves or the like. For example, every 0.2 seconds a container to be sterilized can be delivered , whose inner pressure must be brought to the relevant plasma discharge pressure. The individual pumps are thus not directly connected with the reactors to be evacuated, but rather are connected continuously to the vacuum chambers, to which in turn the reactors to be evacuated are connected successively. Thus the time available for evacuating to the plasma discharge pressure is longer than the tact time in which the individual containers are fed.
In an embodiment of the present invention, the reactors are arranged on the periphery of a rotary runner, which runs through a plurality of stationarily arranged sectors, to each of which a vacuum chamber of differing pressure levels is arranged. The vacuum chambers are hereby in the form of ring channels which rotate with the rotary runners.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings.